1. Field of the Invention
The present invention relates to a method and system for dynamic type ice cold storage of ice crystals as an ice slurry which ice crystals are formed by freezing of an aqueous solution.
2. Description of the Prior Art
As means for leveling, or eliminating, a difference in the demand for electric power between day and night in the summer season, an ice cold storage means which utilizes a surplus electric power in the night time is considered to be effective. In this connection, a dynamic type ice cold storage system capable of freezing an aqueous solution and transporting the resulting ice crystals as an ice slurry up to a place requiring cold is superior in cooling performance during the formation of ice crystals and also in point of reduction in size of the system, but a drawback has been pointed out such that the freezing temperature drops gradually due to an increase in concentration of an aqueous solution with the progress of freezing of the aqueous solution and that therefore the coefficient of performance of the refrigerator used becomes lower and the electric power required for the formation of ice crystals increases.
Accordingly, it is an object of the present invention to provide a dynamic type ice cold storage method and system capable of efficiently suppressing, by an appropriate replenishment of water, an increase in concentration of an aqueous solution with the progress of freezing of the aqueous solution, thereby preventing a lowering in the coefficient of performance of a refrigerator, and hence capable of decreasing the amount of electric power required for the formation of ice crystals.
For achieving the above-mentioned object, in the first aspect of the present invention, there is provided a dynamic type ice cold storage method wherein when an aqueous solution is charged into a freezer which includes a heat exchanger for cooling, allowing an ice slurry containing ice crystals to be formed within the freezer, water is replenished into the freezer in a successive manner in response to a drop in liquid temperature in the freezer so as to keep the freezing temperature in the freezer almost constant.
In the second aspect of the present invention, there is provided, in combination with the above first aspect, a dynamic type ice cold storage method wherein melted water obtained by melting the ice crystals in the freezer at the time of a previous recovery of cold is used as the water which is replenished in a successive manner into the freezer.
Thus, if melted water obtained by melting the ice crystals in the freezer at the time of a previous recovery of cold and which has been stored is utilized, the melted water can be utilized appropriately and repeatedly because it is substantially in the state of pure water containing little solute.
In the third aspect of the present invention, there is provided a dynamic type ice cold storage system comprising a heat exchanger for cooling capable of serving also as a heat exchanger for the recovery of cold, a freezer including the heat exchanger for cooling and capable of serving also as a melter, a thermometer for measuring the temperature of liquid contained in the freezer, an agitator provided in a bottom of the freezer to agitate the liquid contained in the freezer, a mesh stretched horizontally within the freezer at a position somewhat higher than the agitator, an aqueous solution tank connected to the bottom of the freezer through a pipe with valve and also through an aqueous solution pump, and a melted water tank connected to the bottom of the freezer through a pipe with valve and also through a melted water pump.
In the dynamic type ice cold storage system according to the present invention just referred to above, at the time of ice cold storage, first an aqueous solution is fed into the freezer from the aqueous solution tank by means of the aqueous solution pump and an ice slurry containing ice crystals is formed by both freezing action of the heat exchanger for cooling and agitating function of the agitator. In this case, in accordance with a measured value of liquid temperature in the freezer obtained by the thermometer and for the purpose of preventing a drop of the freezing temperature, melting water stored at the time of a previous recovery of cold is replenished into the freezer from the melting water tank by means of the melting water pump and the concentration of the aqueous solution can thereby be maintained in a standard condition, so that the formation of the aforesaid ice slurry can be done efficiently.
Moreover, in the recovery of cold, the freezer is used as a melter and the heat exchanger for cooling is used as a heat exchanger for the recovery of cold. In this case, the aqueous solution contained in the ice slurry is filtered beforehand through the mesh and is stored in the aqueous solution tank, thus permitting repeated use of the above aqueous solution and melted water.
In the fourth aspect of the present invention, there is provided a dynamic type ice cold storage system comprising a freezer including a heat exchanger for cooling, an agitator provided in a bottom of the freezer, a thermometer for measuring the temperature of liquid contained in the freezer, a melter connected to the freezer through a pipe with pump and including a heat exchanger for the recovery of cold, and a mesh stretched horizontally in a bottom of the melter, wherein an aqueous solution tank is connected to the freezer through a pipe with valve and also through an aqueous solution pump, a melted water tank is connected to the freezer through a pipe with valve and also through a melted water pump, and there are further provided a pipe with valve for connecting the bottom of the melter to the aqueous solution tank and a pipe with valve for connecting the bottom of the melter to the melted water tank.
Also in this construction wherein the freezer and the melter are provided separately and are connected with each other through a pipe with valve in the dynamic type ice cold storage system, as is the case with the previous construction wherein the freezer also serves as a melter, at the time of storing ice cold an aqueous solution is fed into the freezer from the aqueous solution tank through the aqueous solution pump and an ice slurry containing ice crystals is produced within the freezer by both freezing action of the heat exchanger for cooling and agitating action of the agitator. In this case, in accordance with a measured value of liquid temperature in the freezer detected by the thermometer and for preventing a drop of the freezing temperature, melted water stored at the time of a previous recovery of cold can be replenished into the freezer from the melted water tank by means of the melted water pump, so that the formation of the aforesaid ice slurry can be done efficiently.
In the recovery of cold, there is used the above heat exchanger for the recovery of cold included in the melter. In this case, the aqueous solution contained in the ice slurry is filtered beforehand through the mesh and is stored in the aqueous solution tank, while the remaining ice crystals are melted by the heat exchanger for the recovery of cold and the resulting melted water is stored in the melted water tank. Thus, the aqueous solution and the melted water can be used repeatedly.
Besides, since the freezer and the melter are connected together through a pipe with pump, even if the place requiring cold is remote from the freezer, it is possible to feed the ice slurry through the said pipe with pump if the pipe with pump is covered with a sufficient cold retaining layer.
In the fifth aspect of the present invention, there is provided, in combination with the above third or fourth aspect, a dynamic type ice cold storage system further including a control system which, in accordance with a detection signal provided from the thermometer, automatically controls the feed of water into the freezer which feed of water is conducted by the melted water pump, for adjusting the concentration of the aqueous solution contained in the freezer.
According to this construction, since the concentration of the aqueous solution in the freezer is thus adjusted in accordance with a detection signal provided from the thermometer which detects the temperature of liquid contained in the freezer, if the feed of water into the freezer by the melted water pump is done automatically by the control system, the operation and management of the dynamic type ice cold storage system are effected accurately in a high efficiency.
Generally, an increase in concentration of an aqueous solution caused by freezing and the resulting decrease of the freezing temperature are widely recognized as a factor of synthetic performance deterioration peculiar to a dynamic type ice cold storage system which uses an aqueous solution. As means for avoiding such an inconvenience, there is adopted a negative and symptomatic means such as (1) lowering an initial concentration of the aqueous solution used or (2) keeping low the amount of ice crystals formed. However, the former involves the problem that the production of an ice slurry (a mixture of solution and ice crystals: ice crystals having fluidity) becomes difficult, thus requiring the development of a new technique for the formation of ice crystals and energy. As to the latter means, it causes a decrease in the proportion of ice crystals contained in a cold storage vessel, i.e., a decrease in the amount of cold stored, thus involving the likelihood that the merits of the dynamic type ice cold storage system may be cancelled.
At present, there has been established no concrete technique for solving the problem induced by an increase in concentration of an aqueous solution with freezing of the solution. For this reason the dynamic type ice cold storage system has not become so popular yet. As noted above, the deterioration in performance of the dynamic type ice cold storage system which utilizes freezing of an aqueous solution is based on a solute concentration effect resulting from freezing of the aqueous solution.
The present invention utilizes the above phenomenon conversely to suppress the deterioration in performance of the dynamic type ice cold storage system. More specifically, with freezing of an aqueous solution, the concentration of the aqueous solution increases due to a solute concentration effect, while ice crystals containing little solute are produced. If the ice crystals are melted at the time of the recovery of cold, there is obtained a substantially pure water, so if this pure water is stored and the aqueous solution is frozen while adding the pure water into the aqueous solution at the time of cold storage, it is possible to keep the concentration of the aqueous solution constant. This is the principle of the present invention.
A major feature of the present invention resides in that, by utilizing a solute concentration effect induced naturally at the time of freezing an aqueous solution, the deterioration in performance of the dynamic type ice cold storage system caused by a drop of the freezing temperature can be suppressed without the use of any additional device or energy.